Rods and rod strings are commonly driven into the ground for a variety of reasons. In conducting cone penetrometer tests, for example, rod strings are sometimes driven 300 or more feet into the ground.
Cone penetrometer systems are commonly used for analyzing subterranean materials and conditions and for developing stratigraphic maps. Recently, cone penetrometer systems have been used in addressing underground contamination problems. Through subsurface analysis, sample recovery, and mapping, cone penetrometer systems have been used to determine the existence and nature of underground contamination problems and to evaluate possible solutions.
A cone penetrometer system will typically utilize a long rod string having a sensing tool, a sampling tool, and/or some other type of tool positioned on the end thereof. The rod string is preferably driven, without drilling or turning, into the ground using a hydraulic ram. For convenience, the hydraulic ram is typically included on a cone penetrometer truck.
In conducting a cone penetrometer test, a relatively small diameter tubing string having a cone tip on the end thereof is typically driven into the ground first. The cone tip can be equipped with electronic sensors which take seismic readings and measure parameters such as: the frictional forces encountered by the rod string during the driving operation; pore water pressure; temperature; inclination; and resistivity. This data is processed and interpreted to obtain a complete stratigraphic map of the test site. Once the stratigraphic data is obtained, the small diameter rod string is typically pulled out of the ground.
Next, a rod string having a sample retrieving tool positioned on the end thereof can be driven into the ground. Sample retrieving tools are used to obtain soil and/or water samples from underground zones of particular interest.
In order to facilitate a rod string driving operation and to allow a rod string to be driven deeper into the ground, a rod string friction reducer can be used. A rod string friction reducer 2 of the type used heretofore is depicted in FIG. 1. Friction reducer 2 is an elongate member having a passageway 4 extending therethrough. Friction reducer 2 includes: a small diameter exterior portion 6 at one end thereof; a small diameter exterior portion 8 at the other end thereof; and a large diameter exterior portion 10 running between exterior portions 6 and 8. An internally threaded portion 12 is provided at one end of friction reducer 2 and an externally threaded portion 14 is provided at the other end of friction reducer 2. Threaded portions 12 and 14 are used for incorporating friction reducer 2 in a rod string. The outside diameters of small exterior portions 6 and 8 are preferably equivalent to the outside diameter of the rod string.
Friction reducer 2 is positioned near the end of a rod string. As the rod string is driven into the ground, friction reducer 2 enlarges the hole produced during the driving operation and thereby operates to reduce the amount of contact which occurs between the ground and the portion of the rod string extending above friction reducer 2. As a result, friction reducer 2 operates to reduce the overall frictional forces encountered by the rod string during the driving operation. Consequently, friction reducer 2 (a) facilitates the driving operation, (b) reduces the amount of stress to which the rod string is subjected during the driving operation, and (c) allows the rod string to be driven deeper into the ground.
In order to facilitate rod string driving operations, a cone penetrometer truck will typically have a guiding sleeve extending through the floor thereof. The guiding sleeve closely contacts and guides the rod string as the rod string is driven into the ground. Additionally, a rod decontamination system, for cleaning the rod string as it is pulled from the ground, will preferably be positioned adjacent the guiding sleeve. A rod decontamination system preferred for use in conjunction with the present invention is disclosed, for example, in U.S. patent application Ser. No. 07/591,347 filed Oct. 1, 1990, the entire disclosure of which is incorporated herein by reference. The decontamination system of U.S. patent application Ser. No. 07/591,347 includes a series of brushes and seals which closely contact the rod string. In order for the decontamination system of U.S. patent application Ser. No. 07/591,347 to be appropriately positioned on the rod string for use during the rod string pulling operation, the rod string is also conducted through the decontamination system as the rod string is driven into the ground.
When a cone penetrometer truck system of the type described above is used for driving a rod string into the ground, a friction reducer 2 of the type used heretofore cannot be connected to the end of the rod string until after the end of the rod string is conducted through the cone penetrometer system (i.e., through the truck's guiding sleeve and/or rod decontamination system). Large exterior portion 10 of friction reducer 2 is too large to travel through a close fitting guiding sleeve or through the close fitting seals of a rod decontamination system.
Since friction reducer 2 cannot be added to the end of the rod string until after the end of the rod string is conducted through the cone penetrometer truck's guiding sleeve and/or rod decontamination system, friction reducer 2, and any tool which is to be included in the rod string beneath friction reducer 2, must be added to the rod string after the end of the rod string is caused to protrude from the bottom of the cone penetrometer truck. In order to provide sufficient room beneath the cone penetrometer truck for connecting friction reducer 2 and the cone penetrometer tool to the end of the rod string, a hole must typically be dug beneath the cone penetrometer truck.
A need presently exists for an improved friction reducing device and method of installation which will eliminate the need to dig holes beneath cone penetrometer trucks. A need also exists for an improved friction reducing device and method of installation which will reduce the amount of rod string assembly and disassembly work which must be performed beneath cone penetrometer trucks.
Additionally, a need presently exists for an improved friction reducing device and method of installation which will allow friction reducers to be incorporated at desired positions along the entire length of a cone penetrometer rod string. As a penetrometer rod string having a single friction reducer 2 positioned on the end thereof is driven into the ground, the large exterior portion 10 of the friction reducer forms a hole having a diameter which is larger than the outside diameter of the upper portion of the rod string (i.e., the portion of the rod string extending above the friction reducer). Thus, as indicated hereinabove, the upper portion of the rod string is not restricted as the rod string is driven into the ground. However, if a portion of the hole collapses, the collapsed material will impinge upon the upper portion of the rod string and increase the amount of frictional drag encountered by the rod string during the driving operation. The amount of frictional drag created by the collapsed material could be reduced by including one or more additional friction reducers in the upper portion of the rod string. However, since the friction reducing device 2 used heretofore can only be added to the end of the penetrometer string after the end of the string is caused to protrude from the bottom of the cone penetrometer truck, additional friction reducers 2 cannot be incorporated in the upper portion of the penetrometer rod string.
A need also exists for an improved friction reducing device which (a) will allow a penetrometer tool to be positioned on the end of a penetrometer rod string before the end of the rod string is delivered through the bottom of the cone penetrometer truck and (b) will allow the penetrometer tool to be pulled, along with the remainder of the rod string, through a rod decontamination system and guiding sleeve. The ability to attach the penetrometer tool to the end of a rod string before the rod string is delivered through the bottom of a cone penetrometer truck would greatly reduce the amount of assembly work which must be performed beneath the truck. In like manner, the ability to subsequently pull the entire rod string, including the penetrometer tool positioned on the end thereof, through the truck's decontamination system and guiding sleeve would greatly reduce the amount of disassembly work which must be performed beneath the truck. Additionally, the ability to pull the penetrometer tool through the decontamination system along with the remainder of the rod string would greatly simplify the decontamination procedure by eliminating the need to disconnect and then separately decontaminate the penetrometer tool.